Out to sea. That sounds like turbulent waves, but that is not the case today, just before the winter intermezzo. It is sunny, almost windless when we sail up the Voordelta at the Brouwersdam in two boats with those involved in the ‘Oyster Coalition’. It is low tide, oystercatchers, curlews and black-backed gulls forage on the dried-up sand, you can still stand 2 kilometers offshore, further away seals are resting on a sandbank.
We are looking for the common oyster, also known as the flat oyster, known from the menu. It seemed for a while that the wild common oyster had almost disappeared from the Dutch delta and the North Sea. Due to disease and overfishing. The oyster is still farmed.
How long do you have to go back in history, what is the reference point, that is always the question, but the fact is that two hundred years ago, one third of the North Sea consisted of shellfish beds. It is also a fact that a large part of the bottom of the North Sea is now a plowed sandbox, and that around 2010 the signal sounded that the native oyster might have ended.
Since then, however, the number of sightings has increased rapidly. In the North Sea, but also in the Oosterschelde, divers found more common oysters every year. There may be a connection with a virus to which Japanese oysters are sensitive, but ordinary oysters are hardly. The two oyster species can coexist, but they compete for the phytoplankton (food) they filter out of the water.
The fact that we are sailing today has to do with a project by ARK Natuurontwikkeling. The nature organization had previously placed empty oyster shells in the western harbor area of Rotterdam, in the hope that larvae of a recently found flat oyster population would attach themselves to them. That happened, and at the end of last year structures made of wire mesh and willow were placed in the sea, containing the shells with attached baby oysters. An attempt to initiate new oyster reef on the North Sea floor. Because ‘reef facilitates reef’, says Ernst Schrijver, marine biologist at the nature organization. Today we are going to see if the ‘oyster cradles’ survived the winter storms.
The common oyster is an ‘enchanting animal’, says Schrijver. Oysters can live to be 30 years old, change sex several times during their lives, and have a form of brood care: the mini larvae that hatch from the fertilized eggs remain ‘inside’ for another ten days. Once outside, the larvae develop for a few more weeks. Schrijver: ‘A swimming pill, with legs. With even weak eyes that can distinguish light and dark.’
After those few weeks, the spat will follow, if all goes well somewhere on a hard substrate, such as an existing oyster bed. Then the oyster becomes a shellfish, and all those oysters together form a bank; that becomes a kind of superorganism that also benefits other species. And they purify, filter the water. ‘Great,’ says Schrijver.
And now we are sitting in the sun on the rippling boat, while diver and biologist Joost Bergsma from the Waardenburg bureau inspects the oyster cradles underwater. Little remains of the structures. They have collapsed and overgrown by mussels, as well as Pacific oysters. This means that most flat oyster larvae probably did not survive. Writer, humbly: ‘Nature once again won’t let itself be taught. Still, it’s nice that the structures are being colonised.’
Then the mysterious thing: a fully-grown wild flat oyster does surface. ‘We haven’t put them out here,’ says Schrijver in amazement. As it turns out: the common oyster is not only enchanting, but also rather inimitable.